1. Field of the Invention
This invention pertains to machinery used in the cutting and shaping of synthetic foam and more particularly is directed to foam cutting machines particularly adapted for the efficient surface contouring of resilient synthetic foam materials, including a cutting machine convertible between such surface contouring and conventional profiling applications.
2. State of the Prior Art
The profiling of compressible synthetic foam is a well known process in which a sheet of resilient foam material is compressed between two profiling rollers and driven against a cutting blade in a compressed condition. The profiling rollers typically have teeth which mesh together in the gap or nip defined between the rollers. The foam compressed between the meshing teeth is sliced along a midpoint in its thickness into two sheets of equal thickness. When the two resulting sheets return to an uncompressed state, the two foam surfaces created by slicing the original sheet expand to define similar surfaces with alternating peaks and depressions which are geometrically complementary to each other.
Profiling machines designed for this purpose are commercially available from several manufacturers. The basic design of all such profilers is similar. Profilers are characterized in that the two rollers are of equal diameter and both rollers have a surface pattern or geometry designed to selectively compress the foam material in accordance with a desired surface geometry of the complementary profiled surfaces created by slicing the thickness of the foam sheet. Another characteristic of such profilers is that the two rollers must be driven in precise step with each other. A mismatch in speed between the rollers results in geometric distortion of the profiled surfaces or actual tearing of the foam. Even a very small difference in relative speed of the rollers causes sufficient distortion to make the resulting foam product commercially worthless. To avoid this problem, conventional profiling machines employ a gear arrangement by which both rollers are synchronously driven by a single drive motor.
U.S. Pat. NO. 5,534,208 discloses a method for shaping resilient foam materials which differs from conventional profiling in that foam material is shaped or contoured to a desired surface geometry by selectively compressing portions of foam material below a cutting blade and cutting away uncompressed portions of the foam. This process differs from profiling in that foam is selectively removed from the existing surface of the original foam blank, and typically the thickness of the desired foam article is substantially the thickness of the original foam sheet. The surface contouring process further differs from conventional profiling in that three dimensional foam surfaces of arbitrary geometry can be produced with a high degree of fidelity because the cutting edge is positioned very near the surface of a pattern or die surface, so that little or no foam thickness is interposed between the pattern surface and the cutting edge. On the other hand, in conventional profiling a considerable thickness of foam is compressed between the profiler rollers and the cutting edge, resulting in a characteristic loss of fidelity of the resulting profiled surface relative to the roller geometry. Sharp edges on the profiler rollers are reproduced as smooth curves on the profiled surface. By contrast, the foam surface contouring process disclosed in the U.S. Pat. No. 5,534,208 patent can closely reproduce a great variety of sharp edged surface geometries not possible by previously known profiling technology. These and other advantages of the proprietary surface contouring process are described in the specification of that patent.
The foam surface contouring process as described in the U.S. Pat. No. 5,534,208 was initially practiced on a conventional, commercially obtained profiling machine adapted for the novel process by substituting a pattern roller and a smooth surfaced backup roller for the conventional profiling rollers. The pattern and backup rollers could be driven by the original unmodified motor drive, so that both rollers were driven at equal speed by the single motor of the original machine. This arrangement was found effective for relatively modest roller speeds and relatively shallow pattern geometries.
For conventional foam profiling the blade is typically spaced significantly in a downstream direction from the point of minimum separation of the rollers, and is also equidistant between the rollers since the foam sheet is to be sliced midway in its thickness. A typical setup is to space the profiling rollers about one inch apart and the cutting blade midway in the gap one half inch from each roller. Furthermore, the spacing of the blade downstream of the point of minimum separation of the rollers is normally not critical within a relatively substantial range of positions.
As explained in the aforementioned U.S. Pat. No. 5,534,208, surface contouring-of the foam material requires that the cutting blade be brought into a tangential position with the pattern roller. For typical surface contouring the cutting edge of the blade is positioned so that little or no foam is removed from the foam blank sheet other than the foam which is pressed into the recesses and depressions defined in the surface of the pattern roller. The optimal location of this tangent point on the pattern roller corresponds to the point of minimum separation between the two rollers and maximum compression of the foam. This requires the blade to be moved forward, i.e. towards the rollers and into actual contact or very near contact with the surface of the pattern roller. The commercial profile cutters permit repositioning of the blade towards and away from the rollers, and also permit the rollers to be individually indexed up or down within the machine frame relative to the blade. Consequently, the cutting edge can be brought into tangential relationship with a pattern roller in the original profile cutter by a combination of roller and blade adjustments.
The surface contouring process of the ""208 patent lends itself to the efficient production of foam articles of many different types. Some articles are cut in one revolution of the pattern roller, and larger articles require a larger pattern circumference. Larger pattern rollers bring out limitations inherent in the commercial machines originally intended for profiling foam. Firstly, conventional profile cutting machines are designed to turn both rollers at the same speed. Consequently, a change in diameter of the pattern roller requires a similar change in the diameter of the compression roller if the original drive mechanism of the profile cutter is used for surface contouring. Also, larger patterns call for roller dimensions greater than those typically used in conventional profiling, until it is no longer possible to bring the cutting blade into optimum tangential position for surface contouring. This happens because of two characteristics common to all known commercially available profile cutting machines. The first is that the cutting blade has a very limited range of adjustment towards and away from the rollers in the cutting plane of the blade, typically about one half inch. The second is that raising and lowering of each roller is done along a corresponding roller indexing guide which is inclined, typically at an angle of 12 to 15 degrees away from the vertical, in a direction away from the cutting blade as the roller is moved away from the cutting plane. This angling of the roller indexing guides is advantageous because as the foam comes under compression between the rollers and the rollers are consequently urged apart, the rollers are not simply forced apart in a direction transverse to the cutting plane, but instead are forced resiliently apart and also slightly away from the cutting blade. The compressive force of the rollers therefore includes a force component which urges the compressed foam towards the edge of the cutting blade and improves the cutting action of the blade.
This geometry of commercially available profile cutters limits their usefulness for purposes of surface contouring applications. As the diameter of the rollers increases the axis of the roller is necessarily supported further away from the cutting plane of the blade. This means that the axes of the rollers are also displaced away from the blade, and the point of minimum spacing between the two rollers is likewise moved further from the blade along the cutting plane of the blade. Because of the limited range of blade adjustment provided in the commercial profile cutters, the point is rapidly reached where for rollers greater than a given diameter it is no longer possible to bring the blade into optimal tangential contact with the pattern roller at or very near the point of minimum spacing between the rollers, where maximum compression of the foam occurs.
While the unmodified commercial profile cutter may be used for surface contouring using smaller pattern roller sizes with equal diameter compression rollers, the full benefit of the surface contouring process calls for a foam cutting machine adapted to the requirements of this process.
The present invention addresses the aforementioned need by providing a foam surface contouring machine which has first and second rollers mounted to a machine frame for rotation about mutually parallel axes, the first and second rollers being of different diameters and defining therebetween a nip; a cutting edge mounted for cutting foam material drawn through the nip by rotation of the rollers; first and second drive motors for driving the first and second rollers respectively; and a controller connected to the first and second drive motors for independently controlling the speed of rotation of the rollers, the controller being adjustable for equalizing the speed of surface rotation of the rollers for first and second rollers of different diameters.
The first roller may be a pattern roller and the second roller may be a backup or compression roller having a substantially smooth cylindrical surface. Typically the pattern roller is of substantially greater diameter than the compression roller. The first and second rollers may be interchangeable with other first and second rollers of different diameters.
In a presently preferred form of the invention the machine has a drive coupling assembly, such as a gearbox, operatively interposed between the drive motors and the rollers. The coupling assembly has selectable first and second modes of operation for converting operation of the machine between foam surface contouring and foam profiling operation. The first mode of operation is operative for independently coupling each of the motors to a corresponding one of the rollers, and the second mode of operation is operative for coupling only one of the drive motors to both of the rollers. In this second mode it is preferred that the two rollers be interlocked for rotation with each other.
The coupling assembly may include a gearbox in which one of the rollers is normally driven by one of the drive motors, and a gear element is selectively repositionable between a first and a second position corresponding respectively to the first and second modes of operation.
For example, the first roller is at all times driven by the first drive motor and, in the first position, the repositionable gear element drivingly engages the second drive motor to the second roller. In this first mode of operation the rollers are driven by the respective drive motors independently of one another. In the second position the displaceable gear element drivingly engages the first drive motor also to the second roller, preferably by mechanically interlocking the second roller for rotation with the first roller. In this second mode of operation both rollers are driven by the first motor only. The repositionable gear element may be displaced between its two positions in an axial direction of the gear element, for example, along a supporting shaft.
These and other features, advantages and improvements according to this invention will be better understood by reference to the following detailed description and accompanying drawings.